Multi-color change device with conductive coating material for electrostatic coating

ABSTRACT

In a color changing apparatus for multiple color electrostatic coating of conductive coating material, a pipe joint (a) provided to be movable and an electrostatic spray gun connected to the pipe joint (a) through a pipeline are provided. A plurality of coating material supply circulation circuits, including a liquid tank, a pump and a pipe joint (b) disengageably engageable with the pipe joint (a) are provided. The liquid tank, the pump and the pipe joint (b) are connected through a pipeline. The pipe joint (a) and the pipe joint (b) in the plurality of coating material supply circulation circuits can be selectively engaged.

RELATED APPLICATIONS

This application is a national phase entry under 35 U.S.C. §371 of PCTapplication number PCT/US00/03926, filed Feb. 15, 2000, which designatedthe U.S., which claims priority under 35 U.S.C. §119, to Japaneseapplication serial number 11-076290, filed Feb. 15, 1999, bothapplications of which are fully incorporated by reference herein.

FIELD OF THE INVENTION

The present invention relates to a color changing apparatus for multiplecolor electrostatic coating which is performed with a conductive coatingmaterial such as an aqueous coating material using an electrostaticcoating spray gun supplied with a high voltage. More specifically, thepresent invention relates to a color changing apparatus for multiplecolor electrostatic coating of conductive coating material, forrealizing easy maintenance of a system other than the system which isbeing used for coating without being influenced by a high voltageapplied and for facilitating color changing.

BACKGROUND OF THE INVENTION

An electrostatic coating method is a technique for applying a highvoltage (generally, 80 to 125 kV) to a corona pin provided in a coatingmaterial spray gun and electrostatically charging the coating materialwhich is sprayed from the spray gun to a high potential so as to applythe coating material on a surface of a subject of coating which isgrounded. Accordingly, when a conductive coating material based on aconductive solvent such as water, methanol or the like is used, aconductive path is formed by the conductive coating material from thespray gun to a coating tank through a coating material supply line. Thecoating material supply system including the coating material tank and apump needs to be insulated from the ground since otherwise the highvoltage is grounded through the coating material supply line and thuscannot be applied to the corona pin provided on the spray gun.

In such an apparatus, high potential electrostatic charges areaccumulated in all the devices from the spray gun and the coatingmaterial supply system. It is very dangerous if the operatorinadvertently contacts a device in the coating material supply systemhaving such a large discharge energy accumulated therein. Therefore, thecoating material cannot even be supplemented to the coating materialtank while the apparatus is in operation. In the case where a colorchanging apparatus for multiple color coating has a structure in which aplurality of coating material supply systems respectively for multiplecolors are directly connected to one another through a switching valveor the like, electrostatic charges are accumulated, through a switchingvalve, even in a coating material supply system for a color other thanthe color which is in use. Thus, the degree of danger is increased, andthe coating material cannot be supplemented even to a coating materialtank for a color other than the color which is in use.

As a method for alleviating these problems regarding color changing formultiple color coating, technologies described. In Japanese Laid-OpenPublication Nos. 4-200663 and 4-200664 are proposed. The technologydisclosed in Japanese Laid-Open Publication Nos. 4-200663 will be firstdescribed. An electrostatic coating apparatus for conductive coatingmaterial which is used for applying a conductive coating material by anelectrostatic coating machine supplied with a high voltage is disclosed.A plurality of pumps are provided in an electrically insulating state,the plurality of pumps having a coating material inflow opening and acoating material outflow opening through which a required amount ofconductive coating material introduced through the coating materialinflow opening is pushed out by pressure at a prescribed flow rate inaccordance with the coating material discharge amount of theelectrostatic coating machine. Detachably connected to the coatingmaterial inflow opening of each of the pumps is a coating materialsupply pipe, which is connected to a respective color changing valveapparatus including a cleaning air supply valve and a cleaning liquidsupply valve. The coating material outflow opening of each pump isconnected to a switching valve for communicating the coating materialoutflow opening to an outflow path on the electrostatic coating machineside or to an outflow path on the exhaust liquid tank side. Each exhaustliquid pipe connected to the exhaust liquid tank is detachably connectedto the outflow path on the exhaust liquid tank side.

The technology disclosed in Japanese Laid-Open Publication Nos. 4-200664will be described. An electrostatic coating apparatus for conductivecoating material which is used for coating a conductive coating materialby an electrostatic coating machine supplied with a high voltage isdisclosed. A plurality of coating material pressure-supply tanks forpushing out a required amount of conductive coatings material storedtherein by air pressure and supplying a constant amount of theconductive coating material to the electrostatic coating machine, and acleaning liquid pressure-supply tank for pushing out a required amountof cleaning liquid stored therein by air pressure and supplying thecleaning liquid to the electrostatic coating machine are provided in anelectrically insulating manner. The coating material pressure-supplytanks and the cleaning liquid pressure-supply tank are connected to therespective color chancing valves provided in parallel to a manifoldcommunicated to the electrostatic coating machine. The coating materialpressure-supply tanks are each provided with a coating materialsupplement opening, and the cleaning liquid pressure-supply tank isprovided with a cleaning liquid supplement opening. The coating materialsupplement opening is detachably connected to a supply pipe forsupplying a conductive coating material of a corresponding color, andthe cleaning liquid supplement opening is detachably connected to acleaning liquid supply pipe.

The above-described conventional technologies, i.e., the technologiesdisclosed in Japanese Laid-Open Publication Nos. 4-200663 and 4-200664have the following problems. The technology disclosed in JapaneseLaid-Open Publication No. 4-200663 has the problems that the circuit isrelatively complicated and accordingly the operation is relativelytroublesome; and each coating material supply system requires twoseparate mechanisms of a coating material supply system and an exhaustedliquid system. The technology further has the following problem.Although not clear from the publication or the figures, a conductivepath is formed, through the conductive coating material, in a pluralityof coating material supply systems (i.e., pumps, coating material tanksand the like) respectively connected to color clanging valves (CV₁through CV₃) of color changing valve devices (9A, 9B, 9C) while thesystems are in use (i.e., connected to the electrostatic coatingmachine). Therefore, none of the color coating materials can besupplemented due to the possible danger of high potentials. Therefore,before supplementing the coating materials, the coating operation needsto be stopped so as to shield the high voltage.

The technology disclosed in Japanese Laid-Open Publication No. 4-200664also has the following problem. A conductive path is formed, through theconductive coating material or the cleaning liquid, even in a pluralityof coating material pressure-supply systems (1A, 2B, 2C) and thecleaning liquid pressure-supply tank (3) while coating is performed.Therefore, none of the color coating materials can be supplemented dueto the possible danger of high potentials. Therefore, beforesupplementing the coating materials, the coating operation needs to bestopped so as to shield the high voltage.

SUMMARY OF THE INVENTION

The present invention made in light of the above-described problems hasan objective of providing a color changing apparatus for multiple colorelectrostatic coating of conductive coating material, which has arelatively simple structure and realizes a relatively simple operation;which separates coating material supply systems other than the systemfor the color which is being used for coating from a circuit chargedwith a high voltage, so as to avoid any influence of the high voltage,so that works such as coating material supplement and maintenance can bedone while the coating is performed; and which realizes easy colorchanging.

In order to solve the above-described problems, the present inventionprovides the following method. In a color changing apparatus formultiple color electrostatic coating of conductive coating material, apipe joint provided to be movable on a guide rail and an electrostaticspray gun connected to the pipe joint a through a pipeline are provided.A plurality of coating material supply circulation circuits, including aliquid tank, a pump and a pipe joint b disengageably engageable with thepipe joint a are provided. The liquid tank, the pump and the pipe jointb are connected through a pipeline. The pipe joint a and the pipe jointb in the plurality of coating material supply circulation circuits canbe selectively disengaged.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may take physical form in certain parts and arrangementsof parts, preferred embodiments and a method of which will be describedin detail in this specification and illustrated in the accompanyingdrawings which form a part hereof, and wherein:

FIG. 1 is a schematic front view illustrating an exemplary colorchanging apparatus for multiple color coating according to the presentinvention; and

FIG. 2 is a schematic side view of FIG. 1.

DESCRIPTION OF THE REFERENCE NUMERALS

1 . . . guide rail; 2 . . . pipe joint a; 3 . . . actuator, 4 . . .electrostatic spray gun; 11 liquid tank; 12 . . . pump; 13 . . . pipejoint b; 14 . . . actuator; 16 . . . pressure adjusting valve; 22 . . .subject of coating.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments of the present invention will be described withreference to FIGS. 1 and 2. According to the present invention, aplurality of coating material supply circulation circuits, i.e., theplurality of coating material supply circulation circuits including aliquid tank, a pump and a pipe joint b which are connected through apipeline can be started, stopped and otherwise operated. A pipe joint aprovided to be movable on a guide rail and an electrostatic spray gunare connected to each other via a one-way pipeline. Accordingly, thecoating material supply circulation circuit associated with the pipejoint b engaged with the pipe joint a is influenced by a high voltageapplied to the electrostatic spray gun through the conductive coatingmaterial. The other coating material supply circulation circuits are notinfluenced by the high voltage since the conductive path is completelydisconnected between the pipe joint a and the pipe join b. Therefore,even while coating is performed, the coating material supply circulationcircuits which are not used can be supplemented with a coating material,even a highly conductive coating material, or subjected to maintenance.

Before changing colors, one of the liquid tanks (for example, tank D)can be filled with a cleaning liquid, and the pipe joint b in thecirculation circuit of the liquid tank D, and the pipe joint a can beconnected to each other while color A is replaced with color B. Thus,the flow system from the pipe joint a to the electrostatic spray gunconnected to the pipe joint a through the pipeline is grounded andcleaned by the cleaning liquid. Accordingly, a color changing operationcan be performed easily without color mixture.

Hereinafter, examples of the color changing apparatus for multiple colorelectrostatic coating of conductive coating material according to thepresent invention will be described by way of drawings. FIG. 1 is aschematic front view illustrating a structure of an exemplary colorchanging apparatus for multiple color electrostatic coating ofconductive coating material according to the present invention; and FIG.2 is a schematic side view of FIG. 1.

In the figures, reference numeral 1 represents a guide rail which can befixed on a support or a wall; reference numeral 2 represents a movablecoupling or pipe joint a provided to be movable on the guide rail 1. Themovable coupling, or pipe joint a 2 is movable on the guide rail 1 by adrive, such as an actuator 3. In this example, a mechanical drive in theform of a hydraulic operable cylinder is used as the actuator 3, but thedrive or actuator can be of other known systems such as an electricsystem. Reference numeral 4 represents a spray device, such as anelectrostatic spray gun having a valve mechanism inside. The spraydevice, or electrostatic spray gun 4, is connected to a high voltagepower supply 5 through a cable 6. A high voltage (80 to 125 kV) isapplied to a corona pin in the electrostatic spray gun 4 to supply anelectrostatic charge to coating material discharged from the spray gun,as desired. The pipe joint a 2 and the electrostatic spray gun 4 areconnected to each other through a supply line, or pipeline, 7. Whenconnecting the pipeline 7 and the pipe joint a 2, the pipe joint a 2moves. It is required they are connected so as not to disturb themovement. Providing a flexible hose or the like may be a simple way torealize this.

In this example, two electrostatic spray guns 4 are provided. The numberof the electrostatic spray guns 4 is not limited to two and can be anynumber in accordance with the conditions of the shape, size and the likeof the subject of coating. When a plurality of electrostatic spray guns4 are provided, each of the electrostatic spray guns 4 is preferablyprovided with a flow rate adjusting valve 8 in order to allow thebalance of the amounts of the coating material from the electrostaticspray guns 4 to be adjusted. Reference numeral 9 represents a dumpvalve; and reference numeral 10 represents an exhaust liquid receptacle.The dump valve 9 and the exhaust liquid receptacle 10 are used forcleaning the inside of the pipeline 7. In the case where the exhaustliquid is recovered in an external recovering container (drum or thelike) although not shown, a dump shuttle, or voltage block, may beprovided to completely electrically insulate the external recoveringcontainer from the systems.

Reference numeral 11 represents a coating material source or liquid tankfor the coating material (one of them is used for the cleaning liquid).A plurality of coating material sources, or liquid tanks 11, areprovided. Four such sources are indicated in the drawings with referencenumerals 11 and representing colors A, B, C and D. Reference numeral 12represents a pump located above the liquid tank 11. Reference numeral 13represents a coating material coupling, or pipe joint, b. Either one ofthe pipe joint b 13 and the pipe joint a 2 is male and the other isfemale so that they are disengageably engaged, or selectively engaged,with each other. The pipe joint a 2 and the pipe joint b 13 are providedwith an internal check valve mechanism for allowing the liquid to flowonly when the pipe joint a 2 and the pipe joint b 13 are engaged witheach other and automatically closing the liquid path when the pipe jointa 2 and the pipe joint b 13 are disengaged from each other. In oneembodiment of the invention, the pipe joint b 13 is connected to theactuator 14 for performing engagement and disengagement by anelectrically insulating material 15 which is interposed therebetween. Inthis example, a hydraulic cylinder mechanism is used as the actuator 14.Of course, an engagement drive, such as a hydraulic cylinder (not shown)can be connected to movable coupling, or pipe joint a 2 to selectively,or disengageably, engage with one of the pipe joints b 13.Alternatively, and also not shown, the movable pipe joint a 2 canselectively engage with one of the pipe joints b 13 only when properlypositioned, and disengage when not so positioned thereby sealing bothpipe joints a 2, b, 13. The pipe joint b 13 is automatically grounded bya ground %%ire at the lowest point where the pipe joint b 13 isdisengaged from the pipe joint a 2. Reference numeral 16 represents apressure adjusting valve, and reference numeral 24 represents acirculation valve.

These devices, i.e., the liquid tank 11, the pump 12, the pipe joint b13, the pressure adjusting valve 16, and the circulation valve 24 areconnected through supply lines, or pipelines 17 and 18 to form thecoating material supply circulation circuit. That is, the conductiveliquid coating material stored in the liquid tank 11 is pumped up by thepump 12 and flows from the coating material supply line, or pipeline, 17to the pipe joint b 13, and then flow through the pipeline 18, thepressure adjusting valve 16 and the circulation valve 24. Then, theconductive liquid coating material returns to the suction side of thepump 12. A part of the conductive liquid coating material returns to theliquid tank 11. During this procedure, the pressure in the coatingmaterial supply circulation circuit is maintained at a prescribed levelby the pressure adjusting valve 16.

When connecting the pipelines 17 and 18 and the pipe joint b 11, thepipe joint b 13 moves up and down in the illustrated embodiment. It isrequired they are connected so as not to disturb the movement. Providinga flexible hose or the like may be a simple way to realize this.Reference numeral 19 represents an insulating material for electricallyinsulating the liquid tank 11. The coating material supply circulationcircuit may undesirably have residual high potential electrostaticcharges even after the pipe joint a 2 and the pipe joint b 13 areseparated from each other. The liquid tank 11 is connected to the relay20 and a grounding circuit 21 for grounding and releasing theelectrostatic charges remaining in the coating material supplycirculation circuit at the time of maintenance. The relay 20 and thegrounding circuit 21 cooperate with the ground wire 23 to form a doublesafe mechanism. A voltage block is thereby formed which electricallyisolates the liquid tank from ground while that liquid tank is beingused in a conductive coating operation and isolates the liquid tank fromthe spray gun while not being used to transmit coating material for acoating operation. Reference numeral 22 represents a grounded subject ofcoating.

In this example, the apparatus includes three coating material supplycirculation circuits including the liquid tank 11, the pump 12, the pipejoint b 13, the pressure adjusting valve 16 and the circulation valve 24which are connected through the pipelines 17 and 18, for convenience.The number of the supply circulation circuits is not limited to threeand can be any number in accordance with the number of colors required.

Next, the function of the color changing apparatus for electrostaticcoating will be described. First the liquid tanks 11 are respectivelyfilled with conductive coating materials A, B and C of different colors.The tank D is assumed to be filled with a cleaning liquid forconvenience, in order to wash the coating material flow path when thecolors are changed. Herein, an example in which coating material A shownin FIG. 1 is applied will be described for convenience. Coatingmaterials of other colors are applied in a similar manner. The actuator3 is operated to position the pipe joint a 2 so as to be engaged withthe pipe joint b 13 of the coating material supply circulation circuitfor an intended color (color A of FIG. 1). Then, the actuator 14 isoperated to engage the pipe joint a 2 with the pipe joint b 13. Then,the high voltage power supply 5 is started and the corona pin of theelectrostatic spray gun 4 is supplied with a high voltage. At thispoint, the dump valve 9 is closed.

When the pump 12 for color A is started, the conductive liquid coatingmaterial A stored in the liquid tank 11 is pumped up by the pump 12 andcirculates in the coating material supply circulation circuit, whichpasses from the pipeline 17 to the pipe joint b 13, then flows throughthe pipeline 18, the pressure adjusting valve 16 and the circulationvalve 24, and returns to the suction side of the pump 12 or the liquidtank 11. Conductive liquid coating material A maintained at theprescribed pressure also flows from the pipe joint b 13 through the pipejoint a 2, the pipeline 7 and the flow rate adjusting valve 8 to reachthe electrostatic spray gun 4. When the valve mechanism incorporated inthe electrostatic spray gun 4 is opened, coating material A is sprayedfrom the nozzle of the electrostatic spray gun 4 and applied on thesurface of the target of coating which is grounded.

The high pressure applied to the electrostatic spray gun 4 influencesall the devices in the coating material supply circulation circuit inthe system of coating material A, in which the conductive path is formedthrough the conductive coating material A. Accordingly, all the devicesin which the conductive path is formed need to be maintained in aninsulating state. Although not shown, the devices need to be enclosed bya protection fence or the like so as to prevent the operator frominadvertently contacting the devices in FIG. 11 in order to maintain allthe devices in an insulating state, the entire system is maintained inan insulating state by the relay 20 of the grounding circuit 21 which isopened, separation of the pipe joint b 13 from the ground wire 23 as aresult of elevation of the actuator 14, and the insulating material 19provided in the liquid tank 11. While coating is performed with coatingmaterial A, the supply circulation circuits for coating material B,coating material C and the cleaning liquid D other than coating materialA are completely separated from the high voltage conductive path at thepipe joint b 13 and also are grounded by the grounding wire 23, theclosed relay 20 and the grounding circuit 21. Thus, these supplycirculation circuits other than the circuit for coating material A arenot influenced by the high voltage.

Next, the process of color chancing will be described. First, in orderto avoid mixing of a color already used and a color to be used, the pipejoint a, the pipeline 7, the flow rate adjusting valve 8 and theelectrostatic spray gun 4 need to be cleaned. Since the cleaningoperation does not need application of a high voltage, the high voltagepower supply is disconnected before the cleaning operation starts. Then,the actuator 14 is operated to disengage the pipe joint a 2 from thepipe joint b 13. Since the pipe joint a 2 and pipe joint b 13 areprovided with a check valve mechanism for preventing liquid leakage, theliquid does not leak.

Next, the actuator 3 is operated to position the pipe joint a 2 so as tobe engaged with the pipe joint b 13 of the cleaning liquid supplycirculation circuit connected to the tank D filled with the cleaningliquid. Then, the actuator 14 of the cleaning liquid supply circulationcircuit D is operated to engage the pipe joint b 13 with the pipe jointa 2. When the dump valve 9 is opened to start the pump 12, coatingmaterial A remaining in the pipeline 7 is pushed out to the exhaustliquid receptacle 10. Thus, the pipeline 7 is cleaned. When the cleaningof the pipeline 7 is finished, the dump valve 9 is closed. When thevalve mechanism incorporated in the electrostatic spray gun 4 is opened,the flow rate adjusting valve 8 and the electrostatic spray gun 4 arecleaned. After the cleaning of the flow rate adjusting valve 8 and theelectrostatic spray gun 4 is finished, the valve mechanism incorporatedin the electrostatic spray gun 4 is closed. Thus, the cleaning operationis completed.

Next, the pipe joint a 2 engaged with the supply circulation circuit forthe cleaning liquid D is separated from the pipe joint b 13. The pipejoint a 2 is moved to be engaged with the pipe joint b 13 of the coatingmaterial supply circulation circuit for coating material B, and the pump12 for coating material B is started to supply coating material B to theelectrostatic spray gun 4. Thus, the color changing from coatingmaterial A to coating material B is completed. A high voltage is appliedto the electrostatic spray gun 4 to open the valve mechanism inside theelectrostatic spray gun 4. Thus, coating material B is applied to thesubject 22 of coating.

By structuring the coating material supply system to be a circulationcircuit having the pipe joint b 13, the pipelines can be engaged ordisengaged at one pipe join, which is significantly simpler than in theconventional structures. The circulation circuits, other than thecirculation circuit which is selected and being used (i.e., thecirculation circuit having the pipe joint b 13 which is engaged with thepipe joint a 2), are completely separated from the high voltage powersupply at the pipe joint b 13 and grounded. Accordingly, thesecirculation circuits can be supplemented with the coating material orsubjected to maintenance even while the apparatus is in operationwithout being influenced by the high voltage. Since electrostaticcharges may undesirably remain from before the separation at the pipejoint b 13, the relay 20 needs to be closed to release the remainingelectrostatic charges through the grounding circuit 21 before themaintenance is started.

As described above, a color changing apparatus for multiple colorelectrostatic coating of conductive coating material according to thepresent invention provides relatively simpler structure and operationthan the prior art apparatuses. The apparatus is structured so that thecoating material color supply systems other than the system for thecolor which is in use are completely separated from the circuit chargedwith a high voltage and thus are not influenced by the high voltage.Thus, eaten while the coating is performed, supplementing of the coatingmaterial and maintenance can be done. The color changing operation isfacilitated.

We claim:
 1. A color changing apparatus for multiple color coating ofconductive coating material, comprising a first pipe joint movable on aguide rail and an electrostatic spray device connected to said firstpipe joint through a pipeline; a plurality of coating material supplycirculation circuits are provided, each including a respective liquidtank for holding a coating material source, a pump and a movable secondpipe joint that can be selectively engaged with said first pipe joint,the liquid tank and the pump and said second pipe joint being connectedthrough a pipeline; wherein when said first pipe joint is selectivelyengaged with one of said plurality of second pipe joints said first pipejoint and the others of said plurality of second pipe joint in theplurality of coating material supply circulation circuits are disengagedfrom each other, wherein at least one of said movable second pipe jointis electrically grounded when disengaged from said first pipe joint andelectrical ungrounded when engaged with said first pipe joint.
 2. Theapparatus of claim 1 wherein at least one of said liquid tanks is forholding a source of electrically conductive, coating material, said atleast one liquid tank is selectively isolated from ground.
 3. Theapparatus of claim 2 further comprising a power supply for applying anelectric charge to said electrically conductive coating materialdischarged from said spray device and a voltage block which electricallyisolates said liquid tank which is transmitting the electricallyconductive coating material to said spray device from electrical ground.4. The apparatus of claim 3 wherein said voltage block electricallyisolates from said spray device said liquid tanks which are nottransmitting coating material to said spray device.
 5. The apparatus ofclaim 1 further comprising a relay for each of said supply circulationcircuits, wherein each of the liquid tanks is selectively electricallyisolated from ground and selectively grounded.
 6. The apparatus of claim1 further comprising a drive for moving the guide rail.
 7. The apparatusof claim 6 wherein the drive comprises a hydraulic operable cylinder. 8.The apparatus of claim 1 further comprising a check valve for each ofsaid pipe joints, such that coating material flow is allowed when saidfirst pipe joint is connected with a respective one of said plurality ofsecond pipe joints and coating material flow is automatically stoppedwhen the respective connected pipe joints are disconnected.
 9. Theapparatus of claim 1 wherein each supply circulation circuit furthercomprises a pressure adjusting valve and circulation valve.
 10. Theapparatus of claim 1 wherein each said movable second pipe joint movesin a direction that is generally transverse a direction of movement ofsaid first pipe joint to engage therewith and disengage therefrom.